The present invention pertains to network connectors and pertains particularly to a low-noise feedback cancellation filter used to enhance common -mode rejection and noise immunity.
When two host systems are communicating via a cable, each host system typically includes a transceiver that converts electrical signals received from the host system to signals that are suitable for the cable. Each transceiver also converts signals received from the cable to electrical signals usable by the host system.
Transceivers used for systems that transfer signals over copper cable must achieve good signal integrity while meeting transmission distance and performance requirements. Signals received by a transceiver have noise from several sources. The sources of noise include ambient noise and crosstalk. Ambient noise is coupled into unshielded twisted pairs (UTPs) of copper cable as they run through noisy environments. Crosstalk occurs as a result of signal leakage across adjacent twisted wire pairs. Additionally, noise can be generated at the signal source. The noise typically shows up equally on both lines of a twisted pair, so the noise can be considered an imbalance, or common-mode component, in what is ideally a purely differential signal. Noise suppression elements are usually present in the front end of the receiver portion of a transceiver. For example, many RJ45 jacks have built-in common-mode chokes and bypass elements.